1. Field of the Invention
The present invention relates to a vehicle crash determining apparatus which controls the starting of an occupant protection means such as an air bag apparatus, a belt pretensioning apparatus or the like which protects the occupants in a vehicle compartment at the time of a vehicle crash.
2. Description of Related Art
FIG. 11 is a plan view showing a state in which a vehicle crash determining means 102 of an occupant protection apparatus is disposed inside a vehicle 101. FIG. 12 is a schematic diagram showing an arrangement of the crash determining means 102 and an occupant protection means 102 has an acceleration sensor 102a, a microcomputer 102b and a starting means 102c. The occupant protection means 103 which is described as an example of an air bag that has a squib (a detonator) 103a which receives an output of the starting means 102c, and an air bag 103b which is inflated upon receipt of the output of the squib 103a. 
A description will now be made about the operation of the above-described arrangement.
The acceleration sensor 102 detects an acceleration due to crashing and outputs an electric signal corresponding to the magnitude of the acceleration. The outputted electric signal is processed as a digital signal through operation by an analog/digital (A/D) converting means. The microcomputer 102b integrates the inputted electric signal by an internally disposed integrating means which is disposed therein with respect to a predetermined section (a predetermined time width). If this integrated value has exceeded a predetermined threshold value, i.e., if a vehicle crash in which the air bag 103b should be started or operated has happened, a determination is made that the crash corresponds to a crash in which xe2x80x9cthe starting of the occupant protection means is necessary.xe2x80x9d
If a determination is made that there has happened a crash in which the air bag 103b should be operated, the starting means 102c is started by the output of the microcomputer 102b. This starting means 102c causes an electric current to flow through the squib 103a, whereby the air bag 103b is operated.
The conventional vehicle crash determining apparatus performs the function of only integrating the acceleration signal detected by the acceleration sensor with respect to the predetermined section. Therefore, in a soft crashing such as an offset crashing or an underride crashing as shown in FIG. 14A, acceleration signals relatively smaller than those in a head-on crashing as shown in FIG. 13A will be continuously outputted for a long period of time. The occupant protection apparatus should ordinarily be operated within this section. However, in case a discrimination is made based on the integrated value between the low-speed head-on crashing and the soft crashing, the predetermined time must be set considerably long as shown in FIGS. 13B and 14B. It follows that the determination for starting the occupant protection apparatus takes a long time. There is therefore a problem in that the occupant protection apparatus cannot be started at an appropriate timing.
This invention has been made in order to solve the above-described problem or the like and has an object of providing a vehicle crash determining apparatus in which a discrimination can be made at a short time between a soft crashing in which relatively smaller acceleration signals last for a long period of time and a low-speed head-on crashing, whereby the occupant protection means can be started at an appropriate timing.
In order to attain the above and other objects, this invention provides a vehicle crash determining apparatus comprising: a first comparing means for comparing an output signal of an acceleration sensor for detecting an impact at a time of crashing of a vehicle with a first threshold value; a second comparing means for determining a necessity of starting an occupant protection means by comparing an accumulated value of an integrating means for accumulating an output of the first comparing means within a predetermined section while making a shift by a unit time with a second threshold value; and a starting means for controlling a starting of the occupant protection means based on an output signal of the second comparing means.
According to another aspect of this invention, there is provided a vehicle crash determining apparatus comprising: a first comparing means for comparing an output signal of the acceleration sensor for detecting an impact at a time of crashing of a vehicle with a first threshold value; a subtracting means for subtracting a predetermined constant value from an output of the first comparing means; an integrating means with a reset function for integrating an output of the subtracting means to thereby forcibly reset an integrated value thus obtained to zero when the integrated value falls below zero; a second comparing means for determining a necessity of starting an occupant protection means by comparing the integrated value of the integrating means and a second threshold value; and a starting means for controlling a starting of the occupant protection means based on an output signal of the second comparing means.
Preferably, the apparatus of this invention may further comprise attenuating means for attenuating a high-frequency component in the output signal from the acceleration sensor to thereby input a resultant product into the first comparing means.